1. Field of the Invention
The present invention relates to an inkjet printer.
2. Discussion of Related Art
An inkjet printer is a sort of image recording apparatus which records an image on a recording sheet as a recording medium by ejecting droplets of ink from a recording head. Thus, ink is needed to be supplied to the recording head.
For example, Patent Document 1 (JP-A-2004-181952) discloses an inkjet printer of a station-supply type in which a sub tank is provided in a carriage carrying a recording head, and an ink cartridge and the sub tank are connected to each other when ink is supplied to the sub tank, and disconnected from each other when ink is not supplied to the sub tank.
Also, Patent Document 2 (JP-A-2004-358918) discloses an inkjet printer including: (1) a sub tank which has a bellows disposed at a position apart from a recording head; (2) a main tank which stores ink in the form of an ink package; (3) a pipe such as a tube which connects the sub tank and the main tank to each other; and (4) an ink supply valve provided in the tube. The ink supply valve is opened or closed so as to control supplying ink from the main tank to the recording head via the sub tank.
For manufacturing an inkjet printer of a station-supply type, the present inventor has experimentally produced and examined a new inkjet printer as a first example different from the respective inkjet printers disclosed in Patent Document 1 and Patent Document 2. The new inkjet printer will be described below.
The new inkjet printer includes a sub tank constituted by an elastically deformable container like a bellows. In the inkjet printer, when ink is supplied to the sub tank, the sub tank is once compressed so that a volume thereof is decreased, and then the volume thereof is expanded and increased to an original state (i.e., a normal state) by an elastic force (i.e., a restoring force) of the sub tank. As a result, ink stored in the ink cartridge is sucked to the sub tank.
A recording head of the inkjet printer ejects a droplet of ink through a nozzle by a pressing means utilizing a deformation of a piezoelectric element or a change in volume of bubbles by a heating resistance element. Normally, a shut-off valve is not provided in the nozzle, and in a waiting state in which ink is not ejected, a meniscus is formed in the nozzle such that a surface of ink is curved inward, with the result that the ink is prevented from leaking out of the nozzle.
Therefore, when the sub tank is expanded in a state in which the meniscus formed in the nozzle is broken, air flows into the sub tank through the nozzle, causing the possibility that an adequate volume of ink cannot be supplied to the sub tank.
Accordingly, the present inventor has experimentally produced and examined another new inkjet printer as a second example which includes a piston pump provided in an ink cartridge for supplying ink stored in the ink cartridge to a sub tank and which operates the piston pump when ink is supplied to the sub tank.
In the second new inkjet printer, since the piston pump is disposed independently of the sub tank, no air flows into the sub tank through a nozzle when ink is supplied to the sub tank. As a result, an adequate volume of ink can be supplied to the sub tank. However, another problem has occurred as mentioned below.
In the second new inkjet printer, the piston pump includes: (a) a cylinder which communicates with a main tank storing ink; (b) a piston which is slidable in the cylinder in a lengthwise direction thereof and cooperates with the cylinder to form a pressure chamber; and (c) a piston rod which is movable integrally with the piston and receives a power to move the piston from a main body side of the inkjet printer and operates the piston to move.
However, in a case in which a new ink cartridge is attached to a frame of the inkjet printer or the piston pump is repeatedly started and stopped, a problem occurs as follows: An actual stop position of the piston when the piston pump is stopped is not aligned with a predetermined initial position (i.e., a zero-point position), so that a volume of ink supplied to the sub tank is changed.
Especially in a full-color inkjet printer including a plurality of ink cartridges, a plurality of piston pumps are needed corresponding to a plurality of inks having respective colors. In a case in which respective actual stop positions of respective pistons of the plurality of piston pumps are not aligned with respective predetermined initial positions and are different from each other, respective volumes of inks supplied to respective sub tanks are changed.